1. Field of the Invention
The present invention relates to a resonator including a resonant tunneling diode (RTD) configured to generate an electromagnetic wave.
2. Description of the Related Art
It has been widely recognized that electronegative resistance elements include a resonator and can be applied for an electromagnetic wave generator. Hitherto, it has been recognized that the electronegative resistance element generates an electromagnetic wave (also referred to as a terahertz wave in this specification) including at least part of frequencies falling within a frequency band of from a millimeter wave band to a terahertz wave band inclusive (from 30 GHz to 30 THz inclusive).
As an example of the electronegative resistance elements, a monolithic resonator including a semiconductor substrate including the RTD, a microstrip conductor, and a grounding conductor, where the semiconductor substrate is sandwiched between the microstrip conductor and the grounding conductor, has been disclosed in Japanese Patent Laid-Open No. 2006-101495. A semi-insulating semiconductor substrate is used as a dielectric serving as an area defined to cause an electromagnetic wave generated through the resonant tunneling diode to resonate.
FIG. 7 is a sectional view illustrating the resonator disclosed in Japanese Patent Laid-Open No. 2006-101495. In the above-described resonator, a resonant tunneling diode hetero structure 10 is stacked on a semi-insulating semiconductor substrate 20. An insulation slab 20 (dielectric) is provided between a microstrip 70 and a grounded metal 30 to cause an electromagnetic wave generated through the resonant tunneling diode to resonate. At that time, the microstrip 70 and a bias pad 60 are connected to the resonant tunneling diode hetero structure 10 through the use of contact layers 80, 90 so that an electrical contact with the resonant tunneling diode hetero structure 10 is achieved. Further, a capacitance is generated through the bias pad 60 and the grounded metal 30 (capacitive coupling). Consequently, an electromagnetic wave of the above-described frequency band can be caused to resonate through a resonator including the microstrip 70, the grounded metal 30, and the insulation slab 20 via the resonant tunneling diode. The above-described configuration allows for reducing a delay time (RC time constant) measured from when a voltage is applied to the resonant tunneling diode to when a current is output from the resonant tunneling diode.